Modeled Thread
Modeled Thread cuts a real helical thread into a round face of the part: on the outside of a shaft, bolt or boss, or on the inside of a hole. Unlike Cosmetic Thread, which only draws a thread, this one removes material, so the volume, the weight and the exported geometry all include the groove. It is one step in the Model tree.
When to Use It
- Show a real thread on a part you will 3D print, so the printed part screws together
- Check the clearance or the weight of a threaded part with the thread in it
- Send a supplier a STEP file with the thread modeled
- Make a left hand thread, such as on a turnbuckle
For a tapped hole or a bolt that a shop will cut anyway, Cosmetic Thread is lighter and faster: the part stays simple and the callout is recorded.
Step by Step
- Open the model for modeling, then click Advanced on the Features tab, then Modeled Thread. The Modeled Thread panel opens.
- Click a round edge in the view: the rim of a hole (an inside thread) or the end of a round shaft (an outside thread). The round face is lit orange.
- The boxes fill in from the closest standard size: the Pitch of that size and a Length of about two diameters. The line under the boxes names the size, says whether the thread is inside or outside, and how many turns it has.
- Change the Pitch, Depth, Length, Start offset and Hand if you need to. Where the thread will run is drawn in orange on the face.
- Click Cut Thread. Cutting takes a few seconds (about half a second a turn). The volume of the part is shown when it is done.
Options
- Pitch: the distance from one thread to the next along the axis. Type threads per inch, like 20 tpi (0.05 in, 1.27 mm), or any length unit, like 0.05 in or 1.5 mm. From 0.0098 in (0.25 mm) up to the diameter of the face.
- Depth: how deep the groove goes into the face, measured straight in from the face. Leave it empty for the usual depth: 0.6134 times the pitch on a shaft and 0.5413 times the pitch in a hole. You can type from 0.05 to 0.75 times the pitch. On a shaft it must also be less than half the shaft's radius. In a hole, at least 0.02 in (0.5 mm) of wall must be left beyond the bottom of the groove all round.
- Length: how far the thread runs along the round face. At least one pitch (one turn), at most 50 turns.
- Start offset: how far from the picked edge the thread begins. Empty or 0 starts it right at the edge. If the start plus the length passes the end of the face by up to 0.008 in (0.2 mm), as a rounded length can, the thread simply runs to the end of the face.
- Hand: Right hand is the usual thread (it tightens turning clockwise). Left hand winds the other way.
The Shape of the Thread
The groove is a plain 60 degree V, the same angle as inch and metric machine threads, with a sharp point at the bottom and no flat at the top. It is a coarse profile: close enough to see, print, weigh and check fits, but not the exact rounded form a thread gauge checks. Inside the part the groove is a triangle as deep as the Depth and 2 x depth x tan 30 degrees (1.155 x depth) wide at the face.
On a 20 mm shaft, a 1.5 mm pitch at the usual depth (0.92 mm) for 15 mm (10 turns) removes about 297.7 cubic mm: 2 x 3.1416 x 10 turns x 0.92 x 0.92 x 0.5774 x (10 - 0.92 / 3). The model matches that within a thousandth (0.1%) when the whole thread lies on the face.
Edit It Later
Right-click the step in the Model tree and choose Edit Feature. You can change the Pitch, Depth, Length, Start offset and Hand in place. Boxes you leave alone keep their exact values. If you change the pitch and leave the Depth box alone, the depth becomes the usual depth for the new pitch; empty the Depth box to get the usual depth at any time. The edge stays the one you picked: to thread another edge, delete the step and make it again. The step is named Modeled Thread and sits in the Bodies group.
Tips and What to Expect
- If an earlier step makes the shaft longer, the thread finds its face again and still starts from the same end.
- A thread that starts at the very end of a shaft runs out into the air there, the way a real cut thread does, so it removes a little less than the full turns would.
- A thread that runs right up to a shoulder or the bottom of a blind hole cuts a little way into it, about half the groove width. Leave a short gap, or set the Length a little shorter.
- Threading one body leaves the other bodies alone, and every body keeps its name.
- The time is capped: if a thread takes longer than 60 seconds to cut when you make it, it is stopped and the part is left as it was. When a saved model is opened or rebuilt, each thread gets 10 minutes, so a slower computer still opens it.
- The thread is cut, so no callout is recorded with it. Add a Cosmetic Thread on the same edge if you also want the callout.
Limits
- One round face per step. A cone or a taper cannot be threaded (no pipe tapers).
- At most 50 turns in one step, and no pitch under 0.0098 in (0.25 mm). For a long or fine thread, use Cosmetic Thread, or make two Modeled Thread steps one after the other, the second one's Start offset where the first one ends.
- The profile is the sharp 60 degree V described above. Square, Acme and buttress threads, and threads with more than one start, are not offered.
Common Problems
- "Click a round edge first: the rim of a hole, or the end of a round shaft." Click the circular edge itself, or the round face near its end.
- "A pitch under 0.0098 in (0.25 mm) is too fine to model." Type a coarser pitch, or use Cosmetic Thread, which draws a fine thread without cutting it.
- "A pitch of ... is too coarse for this round face." The pitch can be at most the diameter of the face. Type a finer pitch.
- "For a ... pitch the depth must be from ... to ..." Sizes are given in inches, then mm. Type a depth in that range, or leave the box empty for the usual depth.
- "That depth would cut more than half way to the middle of this shaft." Type a smaller depth or a finer pitch.
- "That is ... turns; at most 50 are modeled in one step." Make it shorter, use a coarser pitch, or use Cosmetic Thread.
- "The thread runs past the end of the round face." Make the Length shorter, or the Start offset smaller.
- "The thread took longer than 60 seconds to cut." Make it shorter or use a coarser pitch.
- "The wall around this hole is too thin for that thread." Type a smaller depth or a finer pitch, or make the wall thicker.
- "The round face this thread is cut on is no longer on the part." An earlier step changed or removed it. Delete the Modeled Thread step and make it again.